This invention concerns a flowmeter.
A vortex shedding insertion flowmeter is known, e.g. from U.S. Pat. No. 3,587,312, which is arranged for insertion in a fluid conduit and which comprises a tubular member for the passage therethrough of a fluid which flows through said conduit and whose flow rate is to be measured. A bluff body is mounted in the tubular member so as to effect vortex shedding whereby to produce in said fluid oscillations whose frequency varies with said flow rate, there being sensor means responsive to said fluid oscillations for indicating said flow rate.
In known vortex shedding insertion flow meters, however, the pulse/velocity characteristic, i.e. the relationship of the number of pulses per unit time, as sensed by said sensor means, to the velocity of the fluid, is not linear at low flow. We have now found that this phenomenon arises from the fact that vortices are shed both from the bluff body and from the tubular external surface of the tubular member, and that the latter vortices interfere with those from the bluff body itself, so as to affect adversely the flow reading produced by the said sensor means.